Given the composition condition, show that for any birds A, B, and C, there is a bird D such that for every bird x, D(x) === A(B(C(x))).
Assume a bird E that composes B and C:
const E = compose(B, C);Note that, if you call A with E(x) (where x is another arbitrary bird), you get the A(B(C)) nesting we're looking for:
A(E(x)); // => A(B(C(x)));Now we do the same trick again and assume a bird D that composes A with E:
const D = compose(A, E);Thus, D(x) evaluates to A(E(x)) evaluates to A(B(C(x))), regardless of the values of A, B, and C.